This 600 Series Base Unit Technical Service Manual, Part #3756270, has been compiled to provide the most recent information on safety, installation, set-up, design, operation, features, troubleshooting, wiring diagrams, and repair procedures of the 600 Series, prior to Serial #1810000. This information will enable the service technician to trou- bleshoot and diagnose malfunctions, perform necessary repairs, and return a 600 Series unit, prior to Serial# 1810000 to proper operational status.